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Risk of spread of zebra mussel is in the European Commission

• 01.08.2020
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Question for written answer E-003165/2019
to the Commission
Rule 138
Cláudia Monteiro de Aguiar (PPE) and Álvaro Amaro (PPE)
Subject: Risk of spread of zebra mussel

The zebra mussel (Dreissena polymorpha) is a three-centimeter-long bivalve mollusk whose numbers
have increased so much that it can be found in densities of up to 3 million individuals per m2. Once it
is present in an area, it is practically impossible to halt its colonization. Present in Spain since 2001, in
the Ebro, in a few months it spread to two other river basins: the Júcar and the Guadalquivir. Now,
through the Guadiana, the species is threatening the Alqueva, one of the largest reservoirs in Europe,
which supports almost 200 000 hectares of irrigated fields.
By competing for access to phytoplankton, the zebra mussel has a catastrophic environmental impact,
upsetting the ecological balance, and its effluents cover the bottoms of rivers and lakes with a toxic
layer that destroys all the fish in an affected area. Its presence has a knock-on effect on the economy
because it interferes with irrigation systems, power stations’ input and output channels, hydraulic
structures, treatment plants and boats’ engines and anchors.

1. Does the Commission know what measures the Portuguese Government has taken to prevent
and mitigate this infestation?
2. Is the Commission monitoring the spread of the zebra mussel, which is extending its reach in
Spain and is a threat in Portugal?
3. Is the Commission considering providing extraordinary support so that this pest can be tackled?
(Supporters)1
1 Question supported by Members other than the author: Maria da Graça Carvalho (PPE).